Each message, administrative or application, is preceded by a standard header. The header is used to identify the message type, length, destination, sequence number, origination point and time.
Two fields are provided for use when resending messages. The PossDupFlag <43> is set when resending a message as the result of a session level event (i.e. the retransmission of a message reusing a sequence number). The PossResend <97> is set when reissuing a message with a new sequence number (e.g. resending an order). The receiving application should process these messages as follows: